1. Field of the Invention
The claimed invention relates to hydraulic control apparatus, and more particularly to the construction of a dump valve for automatically evacuating entrained solids from a transmission line in response to flow interruption.
2. Description of the Prior Art
It is common practice to convey particulated solids over great distances and elevations by entraining the solids in a fluid transport medium such as a moving stream of water. The entrained solids and water define a slurry which is pumped or otherwise lifted through a transmission conduit at a sufficiently rapid flow rate to prevent settling of the solids in the conduit. When slurry flow is interrupted, the heavier solids, which have a greater specific gravity than the fluid transport medium, settle within the conduit under the influence of gravity. The accumulation of settling solids may cause bridging within the conduit thereby obstructing the flow passage. Additionally, for vertical or substantially inclined conduits, the settling of solids within the conduit may obscure the flow passage to such an extent that it is not practically possible to reestablish slurry flow. Also the descending solids may clog or damage equipment to which the conduit is connected at the lower end. Therefore it is desirable, and in many instances, it is practically necessary to provide means for rapidly evacuating descending solids from a slurry transmission line.
The ability to automatically evacuate or discharge settling solids, without requirement of attention or control, and without providing actuating power, is particularly important where a slurry is being transported upwardly through a great length of conduit from a location which is relatively inaccessible. A good example of such a situation is a deep ocean mining operation in which a marine riser conduit may extend as much as fifteen thousand feet or more from a collector vehicle traversing the ocean floor to a surface vessel. Inasmuch as several tons of nodules may be entrained within the riser conduit, the interruption of slurry flow through the riser conduit will cause immediate bridging as the nodules settle and may possibly damage the collector vehicle. Furthermore, because of the inertia of the large mass of accumulated nodules, it is practically impossible to reestablish slurry flow after a substantial portion of the riser becomes blocked.
The upward movement of slurry within the riser conduit may be interrupted due to a number of causes. For example, the nodules may become temporarily jammed within the riser or be so numerous and close to one another along a length of the riser that the riser flow passage becomes blocked or obstructed. On the other hand, the pump or lift means for inducing slurry flow may fail. Because the riser conduit is pendulously suspended from the surface vessel, it extends substantially vertically downwardly from the surface vessel to the ocean floor. Upon the interruption of the slurry flow, the nodules within the riser having a substantially greater specific gravity settle by gravity flow through the conduit. It is apparent that if all of the nodules were to settle within the riser conduit along a substantial length of the conduit, bridging of the conduit flow passage would occur immediately and the nodule collector vehicle would be subjected to the tremendous mass of the column of nodules accumulated within the riser flow passage. Under such conditions, it is practically impossible to induce the flow of sea water through the riser conduit at a sufficient velocity to re-entrain the nodules and move them upwardly within the riser conduit to the surface vessel.